I have so much trouble with brain fog. In May I forgot to pay the rent. Seriously. Not as in, I kept meaning to write the check and not doing it. As in completely forgot it needed to be done at all.
When applying for SSDI they did some of those mental ability tests on me and I couldn't do them, it almost HURT to try.
Yesterday I did some filing at home, just filing bills into the cabinet and the zillions of papers from worker's comp into their box. Took about 30 mins. It WIPED me out. I broke out into a sweat, couldn't think anymore, felt almost dizzy.

If I'm tired, or trying to do one thing, I can't try to pay attention to anything else. I miss things, forget what was being said etc. I also fall asleep at the drop of a hat if things are complicated (I try to read the news on my computer, sometimes it makes me fall asleep).
I hate it, and I hate not being believed when I try to explain it.